The objective of the proposed research is to elucidate the cellular mechanisms of action of a variety of drugs and toxins on nerve membranes. It is proposed to solve the pharmacological problems by means of sophisticated electrophysiological and biochemical techniques. Special emphases are placed on toxins that exhibit highly specific actions on ionic channels and drugs of clinical importance such as local anesthetics. Detailed kinetic analyses of the interaction between drugs and ionic channels are performed by means of voltage clamp and internal perfusion techniques. Measurements are made of the rate constants of the interaction, the dependencies of the drug action on the membrane potential, exposure time and stimulus frequency, the drug-induced changes in selective ionic permeability, the drug-drug interaction, and the effects on the drug action of environmental factors such as polyvalent cations, pH and temperature. Spin labeled derivatives of local anesthetics and acetylcholine are utilized for the study of drug action with the electron paramagnetic resonance. These data will be integrated at a high level to interpret the mechanism of action of drugs at the membrane and molecular level.